if-then-fi structure in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this Bash script using if-then-fi?

Consider the following Bash script. What will it print when executed?

Bash Scripting

x=5
if [ $x -gt 3 ]
then
  echo "Greater"
fi

A No output

B Less

C Syntax error

D Greater

💡 Hint

Remember the condition checks if x is greater than 3.

The variable x is 5, which is greater than 3, so the condition is true and the echo command runs.

💻 Command Output

intermediate

What happens if the condition in if-then-fi is false?

What will this Bash script print when executed?

Bash Scripting

x=2
if [ $x -gt 3 ]
then
  echo "Greater"
fi

A Greater

B No output

C Syntax error

D 2

💡 Hint

The condition checks if 2 is greater than 3.

Since 2 is not greater than 3, the condition is false and the echo command inside the if block does not run.

📝 Syntax

advanced

Identify the syntax error in this if-then-fi structure

Which option correctly fixes the syntax error in this Bash script?

Bash Scripting

x=4
if [ $x -gt 3 ]
  echo "Greater"
fi

A Replace [ ] with (( ))

B Remove the fi keyword

C Add 'then' after the if condition

D Add a semicolon after echo

💡 Hint

The if statement needs a 'then' keyword before commands.

The 'then' keyword is required after the if condition to start the block of commands.

🚀 Application

advanced

What is the output of this nested if-then-fi script?

Analyze the script and choose the correct output.

Bash Scripting

x=7
y=10
if [ $x -gt 5 ]
then
  if [ $y -lt 15 ]
  then
    echo "Both conditions met"
  fi
fi

A Both conditions met

B Only first condition met

C Only second condition met

D No output

💡 Hint

Both x and y satisfy their conditions.

x is 7 which is greater than 5, and y is 10 which is less than 15, so both if conditions are true and the echo runs.

🔧 Debug

expert

Why does this if-then-fi script fail to run?

What error will this script produce and why?

Bash Scripting

x=3
if [ $x -gt 2 ]
then
  echo "Yes"
else
  echo "No"

A Syntax error: missing fi keyword

B No output

C Runtime error: invalid condition

D Outputs 'Yes' correctly

💡 Hint

Check if the if block is properly closed.

The script is missing the closing 'fi' keyword which ends the if statement, causing a syntax error.

Practice

1. What is the purpose of the if-then-fi structure in a bash script?

easy

A. To run commands only if a certain condition is true

B. To repeat commands multiple times

C. To define a function

D. To declare a variable

Solution

1. Step 1: Understand the role of if-then-fi

   The if-then-fi structure checks a condition and runs commands only if that condition is true.

2. Step 2: Compare with other options

   Repeating commands is done with loops, functions define reusable code, and variables store data, so these do not match if-then-fi.

3. Final Answer:

   To run commands only if a certain condition is true -> Option A

4. Quick Check:

   if-then-fi controls conditional execution = D [OK]

Hint: If you want to do something only when true, use if-then-fi [OK]

Common Mistakes:

• Confusing if-then-fi with loops
• Thinking if-then-fi defines functions
• Using if-then-fi to declare variables

2. Which of the following is the correct syntax for a simple if statement in bash?

easy

A. if $x > 5 then echo "Yes" fi

B. if ($x > 5) { echo "Yes" }

C. if [ $x -gt 5 ]; then echo "Yes"; fi

D. if $x -gt 5 echo "Yes" fi

Solution

1. Step 1: Check the correct if syntax in bash

   Bash requires conditions inside square brackets with spaces, then 'then', commands, and ending with 'fi'. if [ $x -gt 5 ]; then echo "Yes"; fi matches this.

2. Step 2: Identify errors in other options

   if ($x > 5) { echo "Yes" } uses wrong syntax with parentheses and braces (not bash). if $x > 5 then echo "Yes" fi misses semicolons and brackets. if $x -gt 5 echo "Yes" fi misses 'then' keyword.

3. Final Answer:

   if [ $x -gt 5 ]; then echo "Yes"; fi -> Option C

4. Quick Check:

   Correct bash if syntax = C [OK]

Hint: Remember: if [ condition ]; then ... fi with spaces [OK]

Common Mistakes:

• Missing spaces inside [ ]
• Omitting 'then' keyword
• Using wrong brackets or symbols

3. What will be the output of this script?

#!/bin/bash
x=10
if [ $x -lt 5 ]; then
echo "Less"
fi
echo "Done"

medium

A. No output

B. Less
Done

C. Less

D. Done

Solution

1. Step 1: Evaluate the condition

   The variable x is 10. The condition checks if 10 is less than 5, which is false.

2. Step 2: Determine which commands run

   Since the condition is false, the echo "Less" inside if does not run. The echo "Done" after if runs always.

3. Final Answer:

   Done -> Option D

4. Quick Check:

   Condition false, only "Done" prints = A [OK]

Hint: If condition false, skip if block, run commands after fi [OK]

Common Mistakes:

• Assuming if block runs even if condition false
• Confusing -lt with -gt
• Ignoring commands after fi

4. Identify the error in this bash script snippet:

if [ $num -eq 5 ]
then
  echo "Number is five"
fi

medium

A. Missing semicolon or newline after condition

B. No error, script is correct

C. Missing fi keyword

D. Wrong comparison operator

Solution

1. Step 1: Check if syntax correctness

   The condition is inside [ ] with spaces, '-eq' is correct for numeric equality, 'then' is on next line, and 'fi' closes the block.

2. Step 2: Confirm no syntax errors

   Newline after condition is valid instead of semicolon. All keywords are present and correctly placed.

3. Final Answer:

   No error, script is correct -> Option B

4. Quick Check:

   Proper if-then-fi syntax = B [OK]

Hint: Newline after condition is allowed instead of semicolon [OK]

Common Mistakes:

• Thinking newline after condition is error
• Confusing -eq with other operators
• Forgetting fi keyword

5. You want to write a script that prints "Even" if a number stored in n is even, and "Odd" otherwise. Which of these is the correct if-then-fi structure to do this?

hard

A. if [ $((n % 2)) -eq 0 ]; then echo "Even"; else echo "Odd"; fi

B. if [ $n % 2 == 0 ]; then echo "Even"; else echo "Odd"; fi

C. if (( n % 2 == 0 )) then echo "Even"; else echo "Odd"; fi

D. if [ $n / 2 -eq 0 ]; then echo "Even"; else echo "Odd"; fi

Solution

1. Step 1: Understand how to check evenness in bash

   We use arithmetic expansion $(( )) to calculate remainder of n divided by 2. If remainder is 0, number is even.

2. Step 2: Analyze each option's correctness

   if [ $((n % 2)) -eq 0 ]; then echo "Even"; else echo "Odd"; fi correctly uses [ $((n % 2)) -eq 0 ] with then, else, fi. if [ $n % 2 == 0 ]; then echo "Even"; else echo "Odd"; fi uses invalid syntax inside [ ]. if (( n % 2 == 0 )) then echo "Even"; else echo "Odd"; fi misses semicolon before 'then' causing syntax error. if [ $n / 2 -eq 0 ]; then echo "Even"; else echo "Odd"; fi incorrectly uses division instead of modulo.

3. Final Answer:

   if [ $((n % 2)) -eq 0 ]; then echo "Even"; else echo "Odd"; fi -> Option A

4. Quick Check:

   Modulo with $(( )) inside [ ] and proper if-then-fi = A [OK]

Hint: Use $(( )) for math inside [ ] in if-then-fi [OK]

Common Mistakes:

• Using % inside [ ] without $(( ))
• Using == instead of -eq for numbers
• Confusing division with modulo